A control assembly for a nuclear reactor includes a first reactivity control assembly having a first neutron modifying material, a second reactivity control assembly having a second neutron modifying material, and at least one drive mechanism coupled to the first neutron modifying material and the second neutron modifying material. The first neutron modifying material and the second neutron modifying material are selectively repositionable relative to a fuel region of the nuclear reactor. The at least one drive mechanism is configured to provide the first neutron modifying material and the second neutron modifying material in different directions through the fuel region thereby shifting a flux distribution within the fuel region away from the second neutron modifying material.

Methods and systems for in-vessel natural circulation alkali metal reactor systems, purification systems, and associated methods are disclosed. A nuclear reactor vessel system includes an inner vessel that defines an inner volume sized to at least partially enclose a reactor. The reactor includes a plurality of nuclear fuel elements at least partially enclosed within a cladding, the reactor being cooled by a liquid metal coolant in a primary coolant loop. A pool of immersing fluid occupies a volume inside the inner vessel. The reactor vessel system includes an outer vessel sized to wholly or substantially enclose the inner vessel. A nuclear reactor power system includes a reactor core including an active fuel region; and a rotatable drum including at least one of a neutron absorbing material, a neutron leakage enhancing material, or a neutron reflecting material, the rotatable drum positioned external to the active fuel region of the reactor core.

A control rod drive mechanism for use in a nuclear reactor including a reactor core disposed in a pressure vessel, including a control rod configured for insertion into the reactor core, a lead screw, the control rod being secured to the bottom end of the lead screw, a drive mechanism including a torque tube having a top end and a bottom end, a pair of segment arms that are pivotably mounted to the torque tube, a pair of roller nuts, each roller nut being rotatably secured to the bottom end of a respective segment arm, and a drive motor including a stator and a rotor secured to the top end of the torque tube that includes a plurality of permanent magnets embedded therein, wherein the stator defines a central bore in which the rotor is disposed, and a latch coil assembly including a latch coil, wherein the latch coil assembly defines a central bore in which the top ends of the segment arms are disposed radially-inwardly of the latch coil.

A nuclear-reactor control-absorber drive mechanism includes a device for monitoring a potential situation of increase to overspeed of the absorber, configured to measure the number of control steps delivered to at least one of the first, second and third phases of the stator during a time window of preset duration or the number of rotation steps of the rotor during a time window of preset duration. The drive is also configured to compare the number of measured control steps with a preset maximum or the number of measured rotation steps with a preset maximum.

A nuclear-reactor control-absorber drive mechanism includes a device for monitoring a potential situation of increase to overspeed of the absorber, configured to measure the number of control steps delivered to at least one of the first, second and third phases of the stator during a time window of preset duration or the number of rotation steps of the rotor during a time window of preset duration. The drive is also configured to compare the number of measured control steps with a preset maximum or the number of measured rotation steps with a preset maximum.

A cooling system for a nuclear reactor control rod drive mechanism (CRDM) includes an evaporation section located within or next to the CRDM and a condensation section fluidly coupled to the evaporation section. The cooling system may include a set of heat fins that extend up from drive coils in the CRDM and heat pipes that extend through the drive coils and heat fins. A fluid evaporates while in the evaporation section of the heat pipes from heat generated by the CRDM and moves out of the evaporation section into the condensation section in the heat fins. The fluid cools and condensates while in the condensation section, recirculating back into the evaporation section. This passive natural circulation cooling system reduces or eliminates the number of water hoses, piping, and other water pumping equipment typically used for cooling CRDM, or the requirement for air cooling, increasing nuclear reactor reliability and simplifying nuclear reactor operation and maintenance.

Fission reactor has a shell encompassing a reactor space within which are a central longitudinal channel, a plurality of axially extending rings with adjacent rings defining an annular cylindrical space in which a first plurality of primary axial tubes are circumferential located. Circumferentially adjacent primary axial tubes are separated by one of the plurality of secondary channels and a plurality of webbings connects at least a portion of the plurality of primary axial tubes to adjacent structure. A fissionable nuclear fuel composition is located in at least some of the plurality of secondary channels and a primary coolant passes thorough at least some of the primary axial tubes. Additive and/or subtractive manufacturing techniques produce an integral and unitary structure for the fuel loaded reactor space. During manufacturing and as-built, the reactor design can be analyzed using a computational platform that integrates and analyzes data from in-situ monitoring during manufacturing.

A nuclear-reactor control-absorber drive mechanism includes a device for monitoring a potential situation of increase to overspeed of the absorber, configured to measure the number of control steps delivered to at least one of the first, second and third phases of the stator during a time window of preset duration or the number of rotation steps of the rotor during a time window of preset duration. The drive is also configured to compare the number of measured control steps with a preset maximum or the number of measured rotation steps with a preset maximum.

A nuclear-reactor control-absorber drive mechanism includes a device for monitoring a potential situation of increase to overspeed of the absorber, configured to measure the number of control steps delivered to at least one of the first, second and third phases of the stator during a time window of preset duration or the number of rotation steps of the rotor during a time window of preset duration. The drive is also configured to compare the number of measured control steps with a preset maximum or the number of measured rotation steps with a preset maximum.

A sensor assembly for indicating the relative location of a metallic object. The sensor assembly including a primary electromagnetic coil arranged to generate a time varying magnetic field, and a secondary electromagnetic coil arranged to detect the time varying magnetic field as affected, directly or indirectly, by the object and to output, on the basis of the detected time varying magnetic field, a signal indicative of the relative location of the object. At least one of the primary and secondary electromagnetic coils is wound about a core body formed of a material having the same conductivity and/or magnetic permeability as the object.